1. Field of the Invention
This invention relates to an electromagnetic actuator for tilting a surface between angular positions. In particular, this invention relates to mirror actuating devices for rotating a mirror between two angular positions with respect to a rest state, which utilize a single magnet and voice coils, for use in projection systems.
2. Description of Related Art
In the present context, the mirror is moved between two positions in order to double the pixel density of a projected image, by alternating two subframes, each having half of the pixels of the final image. The subframes are slightly offset from each other by the movement of the mirror, for example by having one subframe offset one-half pixel downward relative to the other subframe. The human eye integrates the two consecutive subframes to create the single final image.
While the required mirror rotation is typically very small, it occurs at high accelerations, for example 12G's or more.
In order to realize the forces required, previous motors used in this sort of system have used multiple magnets and numerous moving parts. FIGS. 1A and 1B (Prior Art) illustrate such a prior art device 1 for actuating a mirror in a projector. FIG. 1A shows an assembled device 1 and FIG. 1B shows an exploded view of device 1 of FIG. 1A. In order to accomplish the forces required for mirror actuating, two voice coils 4, four magnets 14, and five pieces of steel (four steel plates 12 and base 16) are required.
As can be seen from the figures, such an assembly comprises many expensive components which are difficult to assemble and due to complexity, might fail during operation.
Therefore a need remains in the art for an electro-magnetic actuator utilizing a simple magnet and coil assembly, for rotating a surface a small amount between angular positions at a high frequency.